Silver has been widely used as an antimicrobial agent for more than 2000 years to create clean drinking water and to prevent infections. The use of silver includes both metallic silver, such as for drinking vessels or tableware, and metal salts, including silver nitrate and silver chloride, that have been used in a wide variety of products ranging from the treatment of infections to the purification of swimming pools. In its ionic form, silver is unique because it attacks infection and odor-causing bacteria through multiple pathways. In addition, silver is immune to acquired antimicrobial resistance that plagues conventional antibiotics.
Recently, silver in the form of silver nanoparticles, silver-containing zeolites, silver salts, other silver-containing compounds, and polymers has found application in medical, consumer and industrial products to reduce the harmful effects of bacteria as well as to prevent odors and other effects from bacteria. The use of finely divided silver metal or weakly soluble silver salts enables efficient release of silver ions in the presence of moisture to provide active protection against undesirable effects of bacteria. The great majority of these active silver-based ingredients are incorporated into these products during the manufacturing process using a range of application methods including: 1) master-batch formulation of, e.g. polymer fibers that incorporate/embed the active ingredients; 2) ion exchange into zeolite particles that are then formulated into final products; or 3) topical coatings that are applied in a manufacturing system. While many of these products have proven to have beneficial properties, their antibacterial properties can wear out long before the textile wears out. In addition, there remains significant challenges related to discoloration of articles treated with silver metal particles (they are typically yellow in color due to plasmon absorption) or silver salts that can significantly darken due to photoreduction. Further, there are very few products available for application and/or reapplication of these benefits directly by consumers.